Development of self-healing and photostimulated luminescent supramolecular polymeric materials is important for artificial soft materials. A supramolecular polymeric hydrogel is reported based on the host–guest recognition between a β-cyclodextrin (β-CD) host polymer (poly-β-CD) and an α-bromonaphthalene (α-BrNp) polymer (poly-BrNp) without any additional gelator, which can self-heal within only about one minute under ambient atmosphere without any additive. This supramolecular polymer system can be excited to engender room-temperature phosphorescence (RTP) signals based on the fact that the inclusion of β-CD macrocycle with α-BrNp moiety is able to induce RTP emission (CD-RTP). The RTP signal can be adjusted reversibly by competitive complexation of β-CD with azobenzene moiety under specific irradiation by introducing another azobenzene guest polymer (poly-Azo).

Photochromic materials are a family of compounds which can undergo reversible photo-switches between two different states or isomers with remarkably different properties. Inspired by their smart photo-switchable characteristics, a variety of light-driven functional materials have been exploited, such as ultrahigh-density optical data storage, molecular switches, logic gates, molecular wires, optic/electronic devices, sensors, bio-imaging and so on. This review commences with a brief description of exciting progress in this field, from systems in solution to modified functional surfaces. Further development of these photo-switchable systems into practical applications as well as existing challenges are also discussed and put in prospect.

A new photochromic compound, S1, containing a trans-cis photoisomerizable unit and a mercury detecting chemosensor unit, has been designed and synthesized. S1 displayed dramatic selectivity for mercury ions over other ions, through fluorescence intensity measurement. In addition, in the photostationary state, a colorimetric response to mercury ions was also achieved. The fluorescence turn-off of S1 by mercury ions was defined as the first check, while mercury-induced colorimetric variation in the photostationary state was set as the second check. Thus, a double-check mercury chemosensor can be achieved.

The photophysical properties of a multicomponent [1]rotaxane bearing a β-cyclodextrin ring covalently connected to an axle comprising an azobenzene photoisomerisable moiety and a naphthalimide-type fluorescent stopper are investigated by a combined experimental and computational study. The absorption and fluorescence spectra, and particularly the induced circular dichroism (ICD) signal, are determined. The latter shows a sign relation that cannot be rationalised in terms of the simple general rules commonly employed to analyse the ICD spectra of achiral guests encircled by chiral hosts. To assist the interpretation of experimental results, DFT and time-dependent (TD) DFT calculations are performed to explore the availability of low-energy conformations and to model their spectroscopic response. Molecular dynamics simulations performed in water show the interconversion of a number of conformers, the contribution of which to the ICD signal is in agreement with the observation.

A series of metal-free organic dyes that were bridged by a diketopyrrolopyrrole moiety and were composed of indoline and triphenylamine as donor groups and furan and benzene as conjugated spacer groups were designed and synthesized for use in dye-sensitized solar cells (DSCs). The photophysical properties, electrochemical properties, and performance of the DSCs were related to the structure of their corresponding dyes. Their absorption spectra broadened upon the introduction of the indoline and heterocyclic furan moieties through fine-tuning of their molecular configuration. The overall conversion efficiencies of DSCs that were based on these dyes ranged from 5.14–6.53 %. Among the four dyes that were tested, indoline-based ID01 and ID02 showed higher efficiencies (6.35 % and 6.53 %) as a result of their improved light-harvesting efficiency and larger electron driving force. The ID01 dye, which contained an indoline moiety as an electron donor and a furan group as a π-conjugated linker, showed an excellent monochromatic incident-photon-to-current-conversion efficiency (IPCE) spectrum (350–650 nm) with a maximum value of 78 % in the high plateau region and an onset value close to 800 nm. Intensity-modulated photovoltage spectroscopy (IMVS) and impedance spectroscopy (IS) revealed that dyes that contained benzene conjugation spacers suppressed the charge-recombination rate more efficiently than dyes that contained furan spacers, thereby resulting in improved photovoltage.

We designed and synthesized the three molecular tweezers 1 a–c⁴⁺ containing an electron acceptor 4,4′-bipyridinium (BPY²⁺) unit in each of the two arms and an (R)-2,2′-dioxy-1,1′-binaphthyl (BIN) unit that plays the role of chiral centre and the hinge of the structure. Each BPY²⁺ unit is connected to the BIN hinge by an alkyl chain formed by two- (1 a⁴⁺), four- (1 b⁴⁺), or six-CH₂ (1 c⁴⁺) groups. The behavior of 1 a–c⁴⁺ upon chemical or photochemical reduction in the absence and in the presence of cucurbit[8]uril (CB[8]) or cucurbit[7]uril (CB[7]) as macrocyclic hosts for the bipyridinium units has been studied in aqueous solution. A detailed analysis of the UV/Vis absorption and circular dichroism (CD) spectra shows that the helicity of the BIN unit can be reversibly modulated by reduction of the BPY²⁺ units, or by association with cucurbiturils. Upon reduction of 1 a–c⁴⁺ compounds, the formed BPY^+. units undergo intramolecular dimerization with a concomitant change in the BIN dihedral angle, which depends on the length of the alkyl spacers. The alkyl linkers also play an important role in association to cucurbiturils. Compound 1 a⁴⁺, because of its short carbon chain, associates to the bulky CB[8] in a 1:1 ratio, whereas in the case of the smaller host compound CB[7] a 1:2 complex is obtained. Compounds 1 b⁴⁺ and 1 c⁴⁺, which have longer linkers, associate to two cucurbiturils regardless of their sizes. In all cases, association with CB[8] causes an increase of the BIN dihedral angle, whereas the formation of CB[7] complexes causes an angle decrease. Reduction of the CB[8] complexes results in an enhancement of the BPY^+. dimerization with respect to free 1 a–c⁴⁺ and causes a noticeable decrease of the BIN dihedral angle, because the BPY^+. units of the two arms have to enter into the same macrocycle. The dimer formation in the CB[8] complexes characterized by a 1:2 ratio implies the release of one macrocycle showing that the binding stoichiometry of these host–guest complexes can be switched from 1:2 to 1:1 by changing the redox state of the guest. When the reduction is performed on the CB[7] complexes, dimer formation is totally inhibited, as expected because the CB[7] cavity cannot host two BPY^+. units.

A novel concept “D-A-π-A” organic sensitizer instead of traditional D-π-A ones is proposed. Remarkably, the incorporated low bandgap, strong electron-withdrawing unit of benzothiadiazole shows several favorable characteristics in the areas of light-harvesting and efficiency: i) optimized energy levels, resulting in a large responsive range of wavelengths into NIR region; ii) a very small blue-shift in the absorption peak on thin TiO₂ films with respect to that in solution; iii) an improvement in the electron distribution of the donor unit to distinctly increase the photo-stability of synthetic intermediates and final sensitizers. The stability and spectral response of indoline dye-based DSSCs are improved by the strong electron-withdrawing benzothiadizole unit in the conjugation bridge. The incident-photon-conversion efficiency of WS-2 reaches nearly 850 nm with a power conversion efficiency as high as 8.7% in liquid electrolyte and 6.6% in ionic-liquid electrolyte.

Time-dependent density functional theory (TD-DFT) with linear and quadratic response approaches was applied to calculate absorption and luminescence spectra of a number of facial and meridional iridium complexes with fluorine-substituted phenylpyridine (F_nppy) ligands. The absorption and luminescence spectra were studied to simulate the photophysical properties of electroluminescent devices fabricated on the basis of these iridium complexes used to increase spin–orbit coupling and the triplet-state blue emission of the corresponding organic light-emitting diodes (OLEDs). By using the quadratic response technique, the phosphorescence radiative rate constant and lifetime of the studied iridium complexes were calculated through spin–orbit coupling perturbation and compared with the measured data in experiments. A satisfactory agreement between these data permits us to guide improvements in the design of phosphorescence-based OLEDs by predicting the structure–property relationships through quantum chemical calculations.

In this work, we have developed a new class of aggregation-induced emission (AIE) active compounds, in which three electron-donating diphenylamine, phenothiazine, or carbazole groups are connected to the 1, 4-positions of the benzene through bis(α-cyano-4-diphenylaminostyryl) conjugation bridges to form three triarylamine quadrupolar derivatives (3 a–c). Their one- and two-photon absorption properties have been investigated. The two-photon absorption (2PA) cross sections measured by the open-aperture Z-scan technique were determined to be 1016, 1484, and 814 GM for 3 a–c, respectively. From this result, the high 2PA properties of these molecules are attributed to the extended π system and enhanced intramolecular charge transfer from the starburst triarylamine to the cyano group. Moreover, cyano-substituted diphenylamine styrylbenzene (CNDPASB)-based compounds are very weakly fluorescent in THF, but their intensities increase by almost 230, 70, and 5 times, respectively, in water/THF (v/v 90 %) mixtures, in which they exhibit strongly enhanced red, orange, and deep yellow fluorescence emissions, respectively. This result indicates that the intramolecular vibration and rotation of these dyes is considerably restricted in nano-aggregates formed in water, leading to significant increases in fluorescence. It was found that the color tuning of the CNDPASB-based compounds could be conveniently accomplished by changing the starburst triarylamine donor moiety. Multilayer electroluminescence devices with TPBI (2,2′,2′′-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole)) electron-transporting layers have been made, with 3 a and 3 c as a non-doping red–yellow emitter. The preliminary results for these multilayer devices show a maximum efficiency of 0.25 %, and electroluminescence (EL) wavelengths around 568 nm. The excellent 2PA and AIE properties of these compounds make them potential materials for biophotonic applications.

Near-IR (NIR) emission can offer distinct advantages for both in vitro and in vivo biological applications. Two NIR fluorescent turn-on sensors N,N′-di-n-butyl-2-(N-{2-[bis(pyridin-2-ylmethyl)amino]ethyl})-6-(N-piperidinyl)naphthalene-1,4,5,8-tetracarboxylic acid bisimide and N,N′-di- n-butyl-2-[N,N,N′-tri(pyridin-2-ylmethyl)amino]ethyl-6-(N-piperidinyl)naphthalene-1,4,5,8-tetracarboxylic acid bisimide (PND and PNT) for Zn²⁺ based on naphthalenediimide fluorophore are reported. Our strategy was to choose core-substituted naphthalenediimide (NDI) as a novel NIR fluorophore and N,N-di(pyridin-2-ylmethyl)ethane-1,2-diamine (DPEA) or N,N,N′-tri(pyridin-2-ylmethyl)ethane-1,2-diamine (TPEA) as the receptor, respectively, so as to improve the selectivity to Zn²⁺. In the case of PND, the negligible shift in absorption and emission spectra is strongly suggestive that the secondary nitrogen atom (directly connected to the NDI moiety, N¹) is little disturbed with Zn²⁺. The fluorescence enhancement of PND with Zn²⁺ titration is dominated with a typical photoinduced electron-transfer (PET) process. In contrast, the N¹ atom for PNT can participate in the coordination of Zn²⁺ ion, diminishing the electron delocalization of the NDI moiety and resulting in intramolecular charge-transfer (ICT) disturbance. For PNT, the distinct blueshift in both absorbance and fluorescence is indicative of a combination of PET and ICT processes, which unexpectedly decreases the sensitivity to Zn²⁺. Due to the differential binding mode caused by the ligand effect, PND shows excellent selectivity to Zn²⁺ over other metal ions, with a larger fluorescent enhancement centered at 650 nm. Also both PND and PNT were successfully used to image intracellular Zn²⁺ ions in the living KB cells.

A conveniently synthesized photochromic compound, BTB-1, containing an unprecedented six-membered 2,1,3-benzothiadiazole unit as the center ethene bridge, possesses good photochromic performance, with a high cyclization quantum yield and moderate fatigue resistance in solution or an organogel system. The fluorescence of BTB-1 can be modulated by solvato- and photochromism. However, the analogue BTB-2, in which the dimethylthiophene substituents are relocated to the 5,6-positions of benzothiadiazole, does not show any detectable photochromism. To the best of our knowledge, this is the first example of six-membered bridge bisthienylethenes (BTEs) in which the photochromism can be controlled by the substitution position. The photochromism difference is elucidated by the analysis of resonance structure, the Woodward–Hoffmann rule, and theoretical calculations on the ground-state potential-energy surface. In a well-ordered single-crystal state, BTB-1 adopts a relatively rare parallel conformation, and forms an interesting two-dimensional structure due to the presence of multiple directional intermolecular interactions, including CH⋅⋅⋅N and CH⋅⋅⋅S hydrogen-bonding interactions, and π–π stacking interactions. This work contributes to several aspects for developing novel photochromic BTE systems with fluorescence modulation and performances controlled by substitution position in different states (solution, organogel, and single crystal).

Three tricarbocyanine dyes (IR-897, IR-877, and IR-925) with different thiourea substituents that function as dosimeter units through specific Hg²⁺-induced desulfurization have been demonstrated in a fast indicator paper for Hg²⁺ and MeHg⁺ ions. In comparison with available Hg²⁺-selective chemodosimeters, IR-897 and IR-877 show several advantages, such as convenient synthesis, very long wavelengths falling in the near-infrared (NIR) region (650–900 nm) with high molar extinction coefficients, a ratiometric response, and quite low disturbance with Ag⁺ and Cu²⁺ ions. They exhibit large redshifts, which result in a clear color change from deep blue to pea green that can be easily monitored by the naked eye for a convenient indicator paper. In emission spectra, they display a characteristic turn-off mode at 780 nm and turn-on mode at 830 nm with titration of Hg²⁺ ions. Remarkably, the signal/noise (S/N) ratio with other thiophilic metal ions (Ag⁺ and Cu²⁺) is greatly enhanced with ratiometric measurement of two channels: excitation spectra mode (I_810 nm/I_670 nm, monitored at 830 nm) and emission spectra mode (I_830 nm/I_780 nm, isosbestic absorption point at 730 nm as excitation). The distinct response is dependent upon the electron-donating effect of the thiourea substituents; that is, the stronger the electron-donating capability of the thiourea substituents, the faster the Hg²⁺-promoted cyclization. Additionally, experiments with living SW1116 cells show that these three tricarbocyanine dyes with low toxicity can exhibit special characteristics that are favorable for visualizing intracellular Hg²⁺ and MeHg⁺ ions in biological systems, including excellent membrane permeability, minimal interfering absorption and fluorescence from biological samples, low scattering, and deep penetration into tissues.